Unnecessarily large satellites cause inefficient use of launch vehicle and satellite facilities and inefficient power management. Moreover, lack of integration among satellite systems leads to undesirable complexity. Thus, excessive payload space and power are consumed by many large, overly complex and redundant systems.
Conventional satellite thermal control systems use a satellite body panel as a primary radiative surface for the satellite. However, body panel size increases as thermal control demands increase, and increased body panel size leads to undesirably large satellites.
A trend in space vehicles, and satellites in particular, is to include an increasing multitude of diverse, complex, non-integrated systems, such as attitude control, payload, propulsion, and the like. This increasing multitude of equipment has increasing cooling requirements. Thus, using body panel size to provide cooling often causes the satellite body or bus to be undesirably large. Since launch cost depends largely on bus size, a significant portion of launch costs are due to thermal control requirements.
The use of a deployable thermal panel can increase a satellite's radiative surface area without needlessly increasing bus size. However, mere deployment of a thermal panel may yield marginal thermal performance. In particular, thermal dissipation during certain orbit positions and at certain times of the year may be undesirably poor. In fact, during some orbit positions, a conventional deployable thermal panel may produce effects opposite of those desired.
Attitude control systems control space vehicle attitude and respond to attitude errors. One cause of attitude error is disturbance torque. Disturbance torques have components about the windmill, overturning, and pitch axes, and cause attitude error which reduces the level of service provided by a satellite. For example, when attitude error of a communications satellite is not corrected, the satellite often compensates for the resultant antenna misalignment by consuming excessive power to transmit communications at higher power. In addition, disturbances due to solar, magnetic, or gravitational influences acting upon momentum wheels cause nutation, a cyclical form of attitude error which recurs at a nutation frequency throughout a satellite's orbit.
Conventional methods of damping disturbance torques involve the use of tanks or magnetic bars on-board the satellite body to slowly absorb the disturbance. However, attitude is not accurately maintained and power is wasted because the solar panels remain improperly oriented with respect to the sun. Propulsion thrusters and momentum wheels are also used to counteract disturbance torques; however, these devices have considerable mass and consume power.
Solar sailing is also used to counter disturbance torques. Unfortunately, conventional solar sailing involves positioning solar panels out of their optimum solar tracking position for as long as six orbital hours at a time. This results in cosine power loss, especially during the solstice periods of the year. Holding the solar panels away from their optimum tracking position also causes significant build-up of secular momentum and excessive variation of cyclical momentum.
Accordingly, what is needed is an actively controlled thermal panel which improves performance of a space vehicle's thermal and other systems.